Investigations of the nitrided subsurface layers of an Fe-Cr-model alloy

An Fe-5 wt%Cr alloy was nitrided in gaseous atmosphere at 590 oC for 12 h. In the resulting diffusion layer, nitrides precipitate on a nanometre scale. The microstructure in the diffusion layer was characterised by optical microscopy and hardness measurements. The morphology, volume fraction and chemical composition of the nitrides were determined by means of atom probe tomography. The orientation of the nitrides with respect to the matrix was investigated using three-dimensional field ion tomography. The evolution of the nitrides was studied at different depths from the surface and their nanoscopic features were correlated with the obtained hardness profile. At a depth of 270 μm from the surface, the first stages of nitride formation could be analysed.